We have been studying the genetic and physical structures of the translocatable DNA elements, IS1 and Tn3 (Amp). Our previous results proved the general involvement of these elements in various recombination events including the fusion of two replicons and deletion formation. We have also characterized the common structural features in these elements. These results enabled us to make predictions concerning the genes and sites within these elements, and to propose several models for the mechanisms of recombination mediated by these elements. We wish to continue to study IS1 and Tn3, focusing on the relationship between the known structural features of these elements and their biological functions, in order to determine the translocation mechanism. To this goal, we study the in vivo recombination between two different plasmids. By assaying the recombination frequency mediated by the elements and their mutants and by analyzing the physical structures of the recombinant DNA with the electron microscope heteroduplex and nucelotide sequencing techniques, we expect to elucidate functional genes and sites of these elements, plasmid genomes, and host chromosomes that may affect recombination mediated by IS1 and Tn3. We also plan to perform biochemical studies on IS1 and Tn3. Analysis of the transcriptional units in these elements and identification of the translated products will substantiate the previous genetic and physical results. We wish to establish a cell free translocation system to follow the biochemical steps of translocation. The knowledge obtained by the cell free system together with the genetic and physical studies should enable us to elucidate the mechanism of translocation. We are also analyzing the repeated DNA sequences present in plasmids and bacteria. Through the studies on repeated sequences including Is1 which flank the unique sequences of resistance and enterotoxin genes in various transposons, we hope to elucidate the generation of resistance bacteria which is a serious problem in medical microbiology.